The ink cartridge detachably mountable to a receiver (cartridge mounting portion) of a main assembly of the ink jet printer is provided with a cartridge side interface portion connectable with an interface portion provided in a main assembly side of the printer (International Publication No. 2012-054050). In International Publication No. 2012-054050, there are provided an electrical contact, an ink supply opening (ink discharge opening, tube inserting opening), a cartridge side locking portion as the cartridge side interface portion. As for the interface portion of the main assembly side of the printer, a receiver is provided with an electrical connecting portion electrically connectable with the electrical contact, an ink receiving tube to be inserted into the ink supply port, a locking mechanism of the main assembly side of the printer for engaging with the cartridge side locking portion. When the ink cartridge is inserted into the receiver, the electrical contact of the ink cartridge is connected with the electrical connecting portion of the receiver, and the ink receiving tube of the receiver is inserted into the supply opening of the ink cartridge. In addition, the cartridge side locking portion is engaged with the locking portion of the main assembly side of the printer, by which the ink cartridge is locked with the receiver. By this, the connection between the ink cartridge and the main assembly of the printer is completed.
As will be understood from FIGS. 6-9 of International Publication No. 2012-054050, the electrical contact is provided adjacent to a right-hand surface of a cartridge parallel with a cartridge mounting direction (Y axis direction). The cartridge side locking portion for fixing the cartridge to the receiver is provided on a cartridge bottom surface far from the electrical contact.